In Situ Determination of Interfacial Energies between Heterogeneously Nucleated CaCO_3 and Quartz Substrates: Thermodynamics of CO_2 Mineral Trapping

摘要

The precipitation of carbonate minerals-mineral trapping-is considered one of the safest sequestration mechanisms ensuring long-term geologic storage of CO_2. However, little is known about the thermodynamic factors controlling the extent of heterogeneous nudeation at mineral surfaces exposed to the fluids in porous reservoirs. The goal of this study is to determine the thermodynamic factors controlling heterogeneous nudeation of carbonate minerals on pristine quartz (100) surfaces, which are assumed representative of sandstone reservoirs. To probe CaCO_3 nudeation on quartz (100) in solution and with nanoscale resolution, an in situ grazing incidence small-angle X-ray scattering technique has been utilized. With this method, a value of α' = 36 ± 5 mJ/ m~2 for the effective interfacial free energy governing heterogeneous nudeation of CaCO_3 has been obtained by measuring nudeation rates at different solution supersaturations. This value is lower than the interfadal energy governing caldte homogeneous nudeation (α ≈ 120 mJ/m~2), suggesting that heterogeneous nudeation of calcium carbonate is favored on quartz (100) at ambient pressure and temperature conditions, with nudeation barriers between 2.5% and 15% lower than those expected for homogeneous nudeation. These observations yield important quantitative parameters readily usable in reactive transport models of nudeation at the reservoir scale.